This invention relates to wound foil electrolytic capacitor sections. More specifically, it relates to tantalum and tantalum-aluminum wound foil sections which are anodized after winding.
Electrolytic capacitors employ metal electrodes on which a thin dielectric oxide of the electrode metal has been formed. Tantalum foil provides many advantages as electrode material including being compatible with electrolytes over a temperature range of about -55.degree. C. to 125.degree. C. with minimum change in resistance and capacitance. It also provides a high capacitance per unit volume. It is more expensive than aluminum foil, however, and one way of reducing capacitor cost has been to use an aluminum foil cathode with a tantalum foil anode as described by Markarian et al. in U.S. Pat. No. 3,654,523 issued Apr. 4, 1972.
Commonly, precut foil strips (which may be etched) are attached to formation bars and inserted into anodization baths to be anodized to the desired voltage and then rinsed and dried. The anodized foil strips with the thin dielectric oxide layer thereon are then convolutely wound with cathode foil and interleaved spacer strips into a tight roll. After impregnation with electrolyte and assembly into the final capacitor, the units must be aged to repair damage to the dielectric oxide film caused by handling, rolling, etc.